The present invention relates to an apparatus for metering, measuring, or dosing flowing media, such as liquids or gases, with said apparatus including: a housing having an inlet and outlet; a chamber that is divided by a metering piston into a first and a second metering chamber; a distributing slide valve that is disposed between the inlet and the outlet in the housing, and that in its two end positions alternately connects the metering chambers with the inlet or with the outlet; a piston rod that is connected to the metering piston and extends in an axially displaceable manner through a larger diameter axial control channel of the slide valve, with the latter being axially movable relative to the piston rod; transfer passages that are disposed in the periphery of the slide valve for controlling the connection of connecting means disposed in the housing to the inlet, the outlet, and the metering chambers; and a transverse connection that is provided in the slide valve to connect the central control channel to the inlet.
DE-A No. 25 49 576 discloses an apparatus of this type where the piston rod is embodied for mechanical operation of the slide valve. For this purpose, in each of the directions of movement, the piston valve acts via a spring-loaded mechanism upon the slide valve, which is arrested in its first end position, and pushes the latter out of this arrested position after the spring-loaded mechanism is tensioned. The spring-loaded mechanism can then relax and effect an accelerated shifting of the slide valve into its second end position, in which the arresting mechanism again engages.
In one end position of the slide valve, the first metering chamber is connected to the inlet via the central control channel and a transverse connection in the slide valve, and the second metering chamber is connected to the outlet via connecting means in the housing and transfer passages in the slide valve. In the other end position, the slide valve connects the first metering chamber with the outlet via the central control channel, and the inlet with the second metering chamber via the connecting means.
Due to the large number of structural elements, the manufacturing costs as well as maintenance costs for the apparatus are very high. Due to the springs that are provided, a specific transfer pressure of the medium is required in order to be able to operate the apparatus. The large number of individual parts lead to a relatively high operating noise, and also result in a high susceptibility to problems and even breakdown, thus practically precluding use of the apparatus, especially with corrosive media.
Pursuant to another known apparatus (DE-B No. 24 02 828), the operation is effected via only a portion of the flowing medium, since the greatest part flows around the control mechanism provided in the housing and is conveyed directly to the outlet, while only a small quantity of the medium that flows in is used to drive the metering piston. The partial quantity is conveyed through a restrictor, resulting in a pressure loss. A further pressure loss occurs in the region of the outlet due to the spring-loaded control valves that are located there and that additionally cause certain striking or chattering noises and are mechanically susceptible. Consequently, this known dosing pump also responds at only high throughput quantities, and also requires a relatively high operating pressure due to the not inconsiderable pressure losses caused by the spring-loaded control valves, so that it is not possible to use this apparatus when the flow through quantities and/or the medium pressure is low.
It is an object of the present invention to improve the known apparatus for metering, measuring, or dosing flowing media in such a way that with a small number of components, a low-noise and low-wear, disturbance-free operation can be assured at a low operating pressure.